Containers intended for containing a still liquid (for example bottles designed to contain table water) are, in most cases, provided with a domed bottom having the general shape of a spherical cap with its concavity facing the outside and of relatively small height. Such bottoms are often provided with radiating ribs spaced apart around a central indentation, it being possible for said ribs to have various conformations and optionally to extend over the base of the wall of the body so as to reinforce the seat (the peripheral region via which the bottom rests on a support). Typically, the height of the bottoms of this kind, central indentation included, is typically around 10 mm, and may be up to 15 mm.
Such bottoms are shaped so as to support, without deforming, the column of flat liquid sitting on top of them. However, they do not have sufficient strength to withstand an additional stress, for example due to internal overpressure, even slight overpressure.
In the case of carbonated liquids (for example those under a pressure of around 3 to 4×105 Pa, or even up to 10×105 Pa), it is known to design containers with a bottom having a much more pronounced curvature (called “champagne” bottom or the like) capable of withstanding high pressures without deforming. However, such bottoms require a larger amount of thermoplastic, both because of their greater height and because of the greater wall thickness, at least locally. Containers provided with such bottoms therefore prove to be more expensive and it is more difficult to shape them correctly during molding.
It is known, when packaging certain easily oxidizable still liquids, to pour a small amount of liquid (for example one drop) of an inert and rapidly vaporizing substance (for example liquid nitrogen) on the surface of the still liquid at the end of the container-filling phase so as to remove the air (and therefore the oxygen contained in the air) from the free volume sitting on top of the liquid surface immediately before stoppering the container (an operation called “inerting”) or to improve the pressurization of the container in the case of lightly carbonated liquids. This small amount of inert substance ends up by being vaporized once the stoppering operation has been completed, so that there remains, in the closed container, some inerting gas under a low residual pressure of less than 2×105 Pa, typically around 1×105 Pa or even around 0.5×105 Pa.
The slightly domed bottoms conventionally provided for containers intended for still liquids are not capable of certainly withstanding, without deforming, a pressure as low as that mentioned above. As regards the use of more resistant bottoms, such as champagne bottoms, their high strength and the additional cost associated with them appear excessive for the envisaged application.